Envisat soars into orbit

Envisat was launched on 1 March 2002 on an Ariane-5 rocket from Europe’s space port in French Guyana. For a decade, Envisat has been keeping watch over our planet.

The eight-tonne satellite, the largest Earth observation satellite ever built, has orbited Earth over 50.000 times in 10 years, delivering thousands of images and a wealth of data to study and understand our changing planet, establishing itself as a landmark success in observing Earth from space.

Although Envisat has been in orbit twice as long as it was designed for, ESA was planning to keep it in service until the next generation of Earth-observing satellites – the Sentinels, under Europe’s Global Monitoring for Environment and Security (GMES) programme – were fully operational.

Unfortunately, communication with the Envisat satellite was suddenly lost on 8 April 2012, just weeks after celebrating its tenth year in orbit. Following rigorous attempts to re-establish contact and the investigation of failure scenarios, the end of the mission was declared on 9 May 2012.

Even after the end of the mission, ten years of archived data from Envisat continue to be exploited for many studies.

The high-tech machine was engineered by a European consortium of companies from 13 countries under the lead of Astrium Germany (MIPAS, Sciamachy) with big contributions for the platform and on the instrumentation side from the UK (ASAR, AATSR) and France (GOMOS).

Envisat had 10 instruments with a wide variety of focuses on board:

• ASAR (Advanced Synthetic Aperture Radar): a radar based on the heritage of the ERS-satellites and ensuring data continuity of these missions. It is the largest single instrument on board and is operating in the C-band. It can acquire images through clouds and darkness.

• MERIS (Medium Resolution Imaging Spectrometer): an imaging spectrometer with a ground pixel size of 300 m recording in 15 spectral bands from the visible to the near infra-red range of the spectrum and able to providing global coverage of the Earth every 3 days. The special feature of MERIS allows the bands to be programmable in width and position.

• AATSR (Advanced Along Track Scanning Radiometer): an infrared radiometer providing high resolution and high accuracy temperature information e.g. for sea surface temperature or fire observation.

• SCIAMACHY: an imaging spectrometer whose primary mission objective is to perform global measurements of trace gases in the troposphere and in the stratosphere.

• MIPAS: A Michelson Interferometer for Passive Atmospheric Sounding looking further into the infrared part of the spectrum and complementing SCIAMACHY providing information on additional trace gases and atmospheric temperatures. The special feature: MIPAS also works at night.

Envisat ready for launch

• GOMOS (Global Ozone Monitoring by Occultation of Stars): dedicated to atmospheric monitoring, GOMOS is a medium resolution spectrometer that primarily measures stratospheric ozone.

• DORIS: The Doppler Orbitography and Radio-positioning Integrated by Satellite instrument is a microwave tracking system that can be utilized to determine the precise location of the Envisat satellite.

• RA-2 (Radar Altimeter): an instrument for determining the two-way delay of the radar echo from the Earth's surface to a very high precision: less than a nanosecond. It also measures the power and the shape of the reflected radar pulses.

• MWR: The microwave radiometer measures integrated atmospheric water vapour column and cloud liquid water content, as correction terms for the radar altimeter signal. In addition, MWR measurement data are useful for the determination of surface emissivity and soil moisture over land, for surface energy budget investigations to support atmospheric studies, and for ice characterization.

• LRR (Laser Retro Reflector): a passive device which is used as a reflector by ground-based SLR stations using high-power pulsed lasers. In the case of Envisat, tracking using the LRR is principally accomplished by the International Laser Ranging Service (ILRS).